You may apply https://www.repairtoolbox.com/addressbookrepair.html Address Book Repair Toolbox if your corruption is complicated or make use of guide below:
Using Explorer find the OE store folder on the new PC's hard drive (HD) by searching for *.dbx. It will be the folder that has inbox.dbx, sent items.dbx, drafts.dbx, etc., in it and unless he moved the store folder to a different location it should be in either
C:\Windows\Application Data\Outlook Express{GUID}
or
C:\Documents and Settings\\Local Settings\Application Data\Identities{GUID}\Microsoft\Outlook Express, where {GUID} is a unique, long, aphanumeric construct like {DC40B654-6026-4B52-AAF7-9998CE175EAF}
Now do the same search for *.dbx on the old HD. Copy all the .dbx files from the old HD folder to the new HD folder, overwriting the default .dbx folders on the new HD. Note that if there are new emails on the new HD, that overwriting will delete those, so if they are important, they should be exported to files before overwriting them. I don't know of a way to merge the two sets of files, but someone else on here might know. Note that it's important that folders.dbx be imported, too, as that contains the folder structure for the emails.
The address book is a little trickier, but it's easier if the same user account name exists on both hard drives.
You can do the same search for *.wab on both drives to find the address book(s). There will be a .wab file for each user and sometimes more than one at different locations. Use the one with the newest date on it, which should be the one that's named .wab, where is his user name on the old HD. Put the desired .wab file from the old HD into the corresponding location on the new HD if it's the same windows user account name, otherwise into the corresponding location of the new user account name, as in
C:\Documents and Settings\\Application Data\Microsoft\Address Book or
C:\Documents and Settings\\Application Data\Microsoft\Address Book
The *.wab files are standalone files and can be accessed by double-clicking on them. That way you can see which the one that he needs is. If there is more than one, some may be empty. On my system the empty ones are 173KB.
Good luck!